From the Appendix B in the NVIDIA driver README:
Option "UseHotplugEvents" "boolean"
When this option is enabled, the NVIDIA X driver will generate RandR display changed events when displays are plugged into or
unplugged from an NVIDIA GPU. Some desktop environments will listen
for these events and dynamically reconfigure the desktop when displays
are added or removed.
Disabling this option suppresses the generation of these RandR events for non-DisplayPort displays, i.e., ones connected via VGA,
DVI, or HDMI. Hotplug events cannot be suppressed for displays
connected via DisplayPort.
Note that probing the display configuration (e.g. with xrandr or nvidia-settings) may cause RandR display changed events to be
generated, regardless of whether this option is enabled or disabled.
Additionally, some VGA ports are incapable of hotplug detection: on
such ports, the addition or removal of displays can only be detected
by re-probing the display configuration.
Default: on. The driver will generate RandR events when displays are added or removed.
So, assuming you have not disabled this option, the problem narrows to one of these alternatives:
The VGA cable or the VGA connector on the card have some DDC pins broken (either pin 12, pin 15 or pin 9). Please attach another VGA cable and try again.
Your Nvidia Quadro K1000M based video card has a connector that does NOT support this detection, and invoking
xrandr or equivalents (as opening the Display Settings) fire this detection. If that is the case, this will never work --but the detection shouldn't work either on other Operative Systems. Never seen this in person, though.
Or maybe there is some bug on the NVIDIA driver that prevents this detection from working properly. Try another driver versions (such as 304) and see if the problem persists.